Modern motor vehicles have internal combustion engines that are running very smoothly so that the operating noise can be hardly heard in the interior of the motor vehicle. The operating sound of the internal combustion engine may be obscured by secondary noises generated by the rolling noise of the wheels, traffic and road noises, fan noises from the vehicle air ventilation system, and the like. The sound insulation for vehicles has also improved to seal out unwanted noise for the occupants. Under certain circumstances it can be desirable to transmit the operating sounds of the internal combustion engine into the interior of the motor vehicle so as to provide the driver with an impression of how the engine in operating and provide an enhanced driving experience.
It is known to utilize a sound transmission tube or duct to conduct or channel sounds from the engine air intake tract toward the passenger compartment. In some cases the sound output of the sound transmission tube is relatively low in volume with the result that it is sometimes desirable to extend the sound transmission tube into the vehicle interior from the engine compartment to thereby improve the transmitted engine sound amplitude level for an improved driver experience.
It is known to provide a flexible diaphragm in the sound transmission tube to provide air flow isolation, thereby preventing air flow through the sound transmission tube. Even if the sound tube is not extended into the passenger compartment, it is undesirable to permit air flow back into the engine air intake tract through a sound transmission tube for which the purpose is strictly to conduct sound. This is especially undesirable if the sound tube is connected to the clean side of the air filter as any air flow through the tube would be introduced as unfiltered air into the air intake tract.
U.S. Pat. No. 7,658,263 discloses a device for noise transmission in a motor vehicle. In this device sound is transmitted along a transmission line having an enlarged mouth at one end and a diaphragm fitted to close off the mouth. A protective device is fitted at the end to protect the diaphragm.
U.S. 2006/0283658 A1 discloses a system for noise increase of an intake system of a motor vehicle. Various possibilities of noise introduction into the interior of the motor vehicle are illustrated wherein the diaphragm is arranged in a pipe conduit for noise transmission.
U.S. 2007/0079784 discloses two hollow sound transmission tubes in sound communication with an air intake tract. The tubes may be brought into the vehicle cabin interior.
JP2000045895A discloses an engine sound transmission system for introducing intake sound into the passage compartment.
However, these sound transmission devices radiate engine noise as a point source. There remains a need in the art for a sound transmission apparatus which evenly and broadly distributes engine sound in the passenger compartment.